I recently bought a nice new Vacuum Guage to test my engines vacuum.
It's a 3.1 MFPI Chevy from 1990. It had 18" hg at idle. BUT, it started to drop to 17", and probably would have went to 16" eventually. It did this VERY slowly, it probably took about 60 seconds to go to 17" hg, and then I removed it.
So the instructions with the gauge indicate that this would normally reveal a "choked muffler" or "restricted exhaust". Is this correct? My ENTIRE exhaust has been changed. The Muffler is brand-new as of 8 months ago, and the Catalytic Converter is about 2.5 years old. The Muffler is OEM, but the Converter was just one of those $100 generic ones.
I have a few other questions, if you don't mind:)?
First, my MAP Sensor fluctuated from 1.7-1.8 volts during the time I was checking the engine vacuum with my gauge. However, this site: Here...
...says that a MAP Sensor should be reading 1.57 volts at 18" hg?
Does anyone know where I can find a GM 1-Bar MAP voltage-vacuum conversion table?? I can't seem to find one by searching Google.
Second, which statement is true:
1-Vacuum leaks are less apparent when COLD than when HOT 2-Vacuum leaks are less apparent when HOT than when COLDThe reason I ask is because I could have sworn I remember a mechanic once telling me that my car(long gone) ran fine in the winter and when it was COLD because I had intake manifold leaks that would get worse(I guess open-up more?) when HOT.
THANKS AGAIN!:)